1. Field of the Invention
In general, the present invention relates to hydrogen diffusion cells. More particularly, the present invention relates to hydrogen diffusion cells that contain wound coils of palladium tubing.
2. Description of the Prior Art
In industry, there are many known techniques for separating hydrogen from more complex molecules in order to produce a supply of hydrogen gas. One such technique is electrolysis, wherein hydrogen gas is obtained from water. Regardless of how hydrogen gas is obtained, the collected hydrogen gas is typically contaminated with secondary gases, such as water vapor, hydrocarbons and the like. The types of contaminants in the collected hydrogen gas are dependent upon the technique used to generate the hydrogen gas.
Although contaminated hydrogen gas is useful for certain applications, many other applications require the use of pure hydrogen. As such, the contaminated hydrogen gas must be purified. One technique used to purify hydrogen is to pass the hydrogen through a hydrogen diffusion cell. A typical hydrogen diffusion cell contains a single coil of palladium tubing. The palladium tubing is heated and the contaminated hydrogen gas is directed through the palladium tubing. When heated, the palladium tubing is permeable to hydrogen gas but not to the contaminants that may be mixed with the hydrogen gas. As such, nearly pure hydrogen passes through the palladium tubing and is collected for use.
Prior art hydrogen diffusion cells that use coils of palladium tubing have many problems. One of the major problems is that of reliability as the hydrogen diffusion cell ages. As a coil of palladium tubing is repeatedly heated and cooled, it expands and contracts. The longer the wound tube is, the more the tube expands and contracts. As the palladium tubing expands and contracts, cracks occur in the tubing. Cracks are particularly prevalent at the ends of the tubing where the palladium tubing is welded to common piping. Once a crack occurs in the palladium tubing or the welded supports of the tubing, the hydrogen diffusion cell ceases to function properly.
The problem of palladium tube cracking is amplified by the manner in which hydrogen gas is drawn out of the hydrogen diffusion cell. In a prior art hydrogen diffusion cell, hydrogen is typically drawn out of one end of the cell. This creates a one-way flow of hydrogen within the confines of the hydrogen diffusion cell as the hydrogen gas flows to one exit point within the cell. Depending upon how rapidly hydrogen gas is drawn from the hydrogen diffusion cell, the flow of hydrogen gas within the confines of the hydrogen diffusion cell can range from a constant mild flow to a sudden severe flow.
As hydrogen gas flows out of such a prior art hydrogen diffusion cell, the flowing hydrogen applies a biasing force to the palladium coils contained within the hydrogen diffusion cell. Over time, the biasing force of the flowing hydrogen physically deforms the palladium coils. The palladium coils become compressed at the end of the coils that are nearest the exit port within the hydrogen diffusion cell. This is because the flowing hydrogen gas biases the palladium coils in the direction of the flow. Likewise, the ends of the palladium coils that face away from the hydrogen gas exit port become stretched as the palladium coils are pulled away by the flowing hydrogen gas. As a result, the palladium coils become stressed in the areas where they are stretched. As the coils expand and contract when heated and cooled, the stressed areas of the palladium coils crack over time and begin to leak. Once a palladium coil begins to leak, the hydrogen diffusion cell is no longer functional.
One solution that has been attempted to increase the reliability of hydrogen diffusion cells is to decrease the length of the palladium tubing and/or the number of windings in the coil of palladium tubing. These techniques reduce the degree of deformation experienced by the palladium tubing caused by the flowing hydrogen gas. However, these techniques also greatly decrease the surface area of the palladium tubing and thus the output and efficiency of the hydrogen diffusion cell.
A need therefore exists for a new hydrogen diffusion cell that has increased reliability yet does not have decreased flow efficiency. This need is met by the present invention as it is described and claimed below.
The present invention is a hydrogen diffusion cell that is used to purify contaminated hydrogen gas. The hydrogen diffusion cell has a supply tube that supplies contaminated hydrogen gas and a drain tube that removes contaminated hydrogen gas. Hydrogen permeable coils are disposed between the supply tube and the drain tube. Disposed in the center of the hydrogen permeable coils is an output tube that collects any hydrogen that diffuses through the hydrogen permeable coils as it flows between the supply tube and the drain tube. The output tube is at least as long as the hydrogen permeable coils and is perforated along its length. In this manner, hydrogen gas is drawn into the output tube throughout the center of the hydrogen diffusion cell. This prevents hydrogen gas from flowing laterally within the hydrogen diffusion cell and deforming the hydrogen permeable coils.